The present invention relates to a lens optical system of an on-board type camera (a camera carried on board of a vehicle), mounted on front and rear side or on lateral side of a moving object such as an automobile, or to a lens optical system of a monitoring camera for taking and recording images inside or outside of a vehicle while a moving object such as an automobile is being driven or is parked. The invention also relates to an image pickup device having lens optical systems of various types of cameras.
In the past, various types of image pickup devices such as an on-board type camera, a monitoring camera, etc. have been known. For instance, in the on-board type cameras disclosed in the Japanese Patent Publications JP-A-2007-163549 or JP-A-2006-11093, an effective field angle in horizontal direction is about 180°. Also, it is about 180° in the image pickup device disclosed in JP-A-2007-328030.
Also, JP-A-2007-163549 discloses a lens system with a second lens group where a plastic lens, a diaphragm, and a plastic lens are arranged with the diaphragm therebetween. In claim 6 of JP-A-2007-163549, lens design is defined on the condition: −0.5<flaf/flar<0 (where flaf and flar represent two focal distances adjacent to each other respectively with a diaphragm between them). In this type of lens design, an effective field angle cannot be attained in horizontal direction.
In JP-A-2006-11093, the conditions are set to: 0.3<|fpnx/fppx|<0.6, and 0.3<|fpny/fppy|<0.6. As a result, in JP-A-2006-11093, an effective field angle cannot be attained in horizontal direction.
Here, when it is assumed that optical axis is Z-axis and that X-axis and Y-axis perpendicularly cross the Z-axis, it is defined as follows:                fpnx: X-Z section paraxial focal distance of a negative lens made of plastic material;        fppx: X-Z section paraxial focal distance of a positive lens made of plastic material;        fpny: Y-Z section paraxial focal distance of a negative lens made of plastic material; and        fppy: Y-Z section paraxial focal distance of a positive lens made of plastic material.        As a described above, in the conventional type image pickup device, an effective field angle is about 180°, and it is not possible to attain the effective field angle to 200° or more at maximum in horizontal direction. Further, it is not possible to accomplish an anamorphic optical system with high projection characteristics and high resolving power in particular, and it is not possible to realize anamorphic magnification, which is not influenced by temperature conditions, either.        